The morphology and staining characteristics of blood mononuclear cells in injured nervous tissue will be compared to that of the cells which proliferate in response to injury. The relationship of blood mononuclear cells to microglia and to reactive astrocytes will be investigated. BIBLIOGRAPHIC REFERENCES: Adrian, E.K., Jr., and F.C. George, Fine structure of cells in the hypoglossal nucleus labeled with H3-thymidine injected before transection of the hypoglossal nerve. Anat. Rec. 181: 298, 1975.